Image sensors are desired to provide high-resolution, high signal-to-noise, and accurate color representations of visual scenes. Frequently, image sensors offer color discrimination using a pattern of color filters, such as the often-employed Bayer Pattern (GR/BG), a 2×2 array.
As pixel sizes are reduced to accommodate more pixels per integrated circuit area, thereby increasing resolution while containing cost, it becomes increasingly challenging to accommodate all electronic devices, such as transistors, that are needed to provide reset, charge accumulation and storage, transfer, shuttering, etc., within the pixel area. Therefore, it is desirable to provide layouts of pixels that can enable additional transistors to be accommodated, or to allow a given number of transistors to be accommodated within a reduced area.
Additionally, microlenses are often employed in image sensors, with one goal being to focus light through the relevant color filter array region, a strategy that reduces color crosstalk associated with optical color filter array (CFA) crosstalk. Fabrication methods of microlenses atop a square-symmetry array often produce regions at the microlens corners that are not effective in light focusing, contributing to a loss in fill factor (hence sensitivity) and also a loss of color discrimination (hence larger matrix elements in the color correction matrix, hence lower signal-to-noise ratio (SNR) in the final de-mosaiced color image).
One approach to ensure maximally effective microlenses is to provide a layout of pixels that comes closer to providing circular symmetry in the layout of the pixels. This may be achieved by increasing the number of nearest-neighbors, such as in a hexagonal array instead of a square array.
Embodiments are described, by way of example only, with reference to the accompanying drawings. The drawings are not necessarily to scale. For clarity and conciseness, certain features of the embodiment may be exaggerated and shown in schematic form.